Two-sided substrate imaging using single-approach projection optics

ABSTRACT

Apparatus and method for side-by-side scanning of substrate panels to use a single-approach projection optical system to provide a patterned image on each of two substrate surfaces. More particularly, the system provides a technique for pattern scanning obverse and reverse surfaces, patterning one substrate surface, inverting the substrate panel and repositioning the substrate panel for patterning the opposite substrate surface. The inversion provides access to both surfaces of a substrate panel for pattern scanning by the same optics and the same precision x-y stage in quick succession. The system positions the same substrate panel inverted, or another substrate panel, as required, twice at one station or sequentially at first and second stations. The flipping mechanism may be a simple grabber/retractor with a rotatable wrist for substrate inverting; the stage selects the imaging station. Forwarders may be Inexpensive standard pick-and-place, slide-shuttle or carousel loader/unloader mechanisms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application number 09/520,393, filedMar. 8, 2000, now U.S. Pat. No. 6,356,337, Zemel, TWO-SIDED SUBSTRATEIMAGING USING SINGLE-APPROACH PROJECTION OPTICS, Mar. 12, 2002.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

(Not Applicable.)

REFERENCE TO A MICROFICHE APPENDIX

(Not Applicable.)

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a technique to provide high-resolutionpatterned images on each of obverse and reverse (generally top andbottom) surfaces of substrate panels using single-approach projectionoptics and a scanning stage, and more particularly relates to apparatusand method for flipping the substrate over, to provide access to asecond surface of the substrate for pattern scanning, while retainingthe registration and resolution advantages of having obverse and reverseof each substrate panel patterned in quick succession with the sameprojection optics scanned by the same stage carriage.

(2) Description of Related Art

State of the art microelectronics patterning systems follow the lead ofU.S. Pat. No. 4,924,257, Scan and Repeat High Resolution LithographySystem, Jain, May 08, 1990. Dr. Jain teaches the use of a treated beamof laser radiation for patterning a substrate according to a mask, bothmask and substrate being scanned line-by-line by a small hexagonal fieldin overlapping complementary scans, for balanced illumination of themask pattern on a photoresist on the surface of the substrate.

The desire to form such microlithographed patterns on both surfaces of asubstrate, typically a thin, flat, non-flexible printed circuit board ormicrochip, is both stated and solved in U.S. Pat. No. 5,923,403.Simultaneous, Two-Sided Projection Lithography System, Jain, Jul. 13,1999. Jain splits the radiation beam of a laser, and by light-beamdirecting projection optical systems applies patterning radiationsimultaneously through separate masks to both sides of the flatsubstrate. The obverse and reverse surfaces of a substrate panel aresimultaneously patterned by dual optical projection systems. One of theoptical projection systems has an up-approach, through a see-throughwindow in the stage carriage. The other optical projection system has adown-approach.

There is another way to divide the laser beam. U.S. Pat. No. 5,933,216,Double-Sided Patterning System using Dual-Wavelength Output of anExcimer Laser, Dunn, Aug. 3, 1999, splits the laser beam into twodifferent peak-power wavelengths and forwards the separated beams alongseparate optical projection systems for the two sides of the substrate.The differing wavelengths of radiation require either a broadbandphotoresist or a separate photoresist for obverse and reverse, eachoptimized for a respective one of the two wavelengths. Two substratesmay be accessed at one time, in one embodiment by up-approach anddown-approach projection optical systems—and in another embodiment byside-by-side down-approach projection optical systems, but for singlesides only of the two substrate panels.

BRIEF SUMMARY OF THE INVENTION

The two-sided projection lithography systems identified above providefor very high quality two-sided microelectronics patterning, mutuallyregistered, with high throughput. They are most cost-effective inrelatively long production runs. There remains, however, a continuingdesire for simplicity and economy in two-sided high-resolutionpatterning, both aspects being economized by having single-approachoptics and a simple stage carriage, with 1:1 projection optics, for maskand substrate.

The desire continues for a simple system for high-resolution patterningof two-sided substrates, which has a single set of projection opticalsystem, provides easy two-side registration, and is economical forrelatively short patterning runs.

It is the object of the invention to provide, in a novelmicroelectronics patterning system, electromechanical positioners toflip the substrates for economical two-side high-resolution patterningby a single set of projection optics.

Another object of the Invention is to provide a novel method forpositioning and repositioning substrates for two-sided patterning,during a single production run, by flipping the substrates forpatterning by a single-approach set of projection optics.

A feature of the invention is the use, in a simplified embodiment, of asingle feeder/flipper/forwarder to load, flip, reposition and unload thesubstrate panels on the stage carriage which provides scanning motion ofthe substrates with respect to the projection optics and the masks.

Another feature of the invention is the use, in a second embodiment inwhich the economics favor separate feeders for loading and unloading,and a flipper/forwarder for repositioning the substrate after the firstside has been patterned, for patterning the second side.

An advantage of the invention is that the costly portions of the systemdo not have to be replicated, but rather are time-shared as a result ofthe inventive hardware and method.

Another advantage is that there is no need for a see-through window inthe stage carriage, allowing for simpler and more powerful substrategrasp by vacuum.

A significant advantage in economy arises from the ease with which thisinvention can be retrofitted on existing single-approach lithographysystems, by alteration of programming in the control computer togetherwith addition of relatively inexpensive flipper mechanisms to existingsubstrate feeder mechanisms, or by replacement feeder/flipper/forwardermechanisms.

Other objects, features and advantages of the invention will be apparentfrom the following written description, claims, abstract and the annexeddrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a perspective view of the system.

FIG. 2 is a partially schematic side elevation view, showing how masksand substrate panels are gripped during patterning exposures.

FIG. 3 is a perspective view of a preferred feeder/flipper/forwarder(loader/unloader) for the system.

FIG. 4 is diagrammatic perspective view of flipper/forwarder flippingmotions.

FIG. 5 is a schematic view of simplified flipper motions.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of the system, showing projection optics 1and stage 2. Stage 2 provides scanning motion with respect to optics 1.Two masks 3 (each mask carrying a first pattern 3-1 or a second pattern3-2) are shown locked in place on stage 2. Stage 2 also carries one ortwo substrate panels 4 in patterning positions. Each substrate panel 4has a first (obverse) side 4 _(o) and a second (reverse) side 4 _(r).Two substrate panels SP1 and SP2 are in patterning positions for 4 _(o)and 4 _(r) are shown. Postulate that patterning has been completed onboth surfaces of substrate SP1, which is ready to be removed. The usualintent is to project separate pattern images of ultraviolet radiation,patterned according to separate obverse pattern mask and reverse patternmask, onto photosensitive layers on the obverse and reverse of eachsubstrate, to characterize a microcircuit pattern. Procedures may vary,but the usual procedure is to:

unload/flip/forward/load substrate panels;

project the image of the obverse pattern 3 o onto obverse side 4 o ofthe substrate panel 4 at patterning station SP1 and project the image ofthe reverse pattern 3 r onto the reverse side 4 r of the substrate panel4 at patterning station SP2;

then flip the substrate panel at SP1 over, preferably to a new position,SP2, on the vacuum-operated substrate chuck carriage 5 of stage 2; andthen

project the image of the obverse pattern 3 o onto obverse side 4 o ofthe substrate panel 4 at patterning station SP1 and project the image ofthe reverse pattern 3 r onto the reverse side 4 r of the substrate panel4 at patterning station SP2; and

repeat for each of the substrates SP1, SP2 . . . SPn until allsubstrates SP1, SP2 . . . SPn have been patterned on both obverse andreverse surfaces.

This procedure continues, as substrates SP1, SP2 . . . SPn are in turnloaded, patterned, flipped, patterned, and unloaded. Substrates SP1, SP2. . . SPn are taken from a supply/return rack 6, mounted on stage 2carriage 5 in position for pattern imaging, patterned, flipped,patterned, unloaded and returned to supply/return rack 6. The patterningradiation beam, from laser 7, passes along beam-directing subsystem andthrough a scan path in one of masks 3 o and 3 r. (Reverse mask 3 r isshown in patterning position in FIG. 1, providing the reverse-sidepattern to substrate SP2, The patterning radiation beam is patternedaccording to the mask (mask 3 r is shown in position). The mask 3 r andreverse side of substrate SP2 are scanned line-by-Line, preferably inthe overlapping complementary scans of previously cited U.S. Pat. No.4,924,257, Jain.

FIG. 1 postulates that the obverse side of substrate panel SP1 is readyto be patterned according to the pattern on mask 3 _(r), and that afully-patterned substrate panel SPO (not shown) has been previouslyreturned to the supply/return rack 6. FIG. 1 also showsfeeder/flipper/forwarder (loader/unloader) 8 for the system, and controlunit 9. FIG. 1 shows stationary base 10, which typically is a heavyvibration-damping block which supports projection optics 1 by a bridge11-12, provides the base for the feeder/flipper/forwarder(loader/unloader) 8, supports the supply/return rack 6 and supports thebase of the stage 2. Feeder/flipper/forwarder 8 serves as means havingthe capability of inverting a substrate panel taken directly from asubstrate chuck on a carriage and forwarded directly to a substratechuck on said carriage.

FIG. 2 is a side elevation view, partially schematic, showing how thesubstrate panels and masks are supported for presentation. Masks 3 (withmask patterns 3 _(o) & 3 _(r)) and substrates (SP1, SP2 . . . SPn) arecarried on mask/substrate carriage 5. Mask/substrate carriage 5 istransparent to the activating radiation in the active area of the mask.Each mask 3 is held in place by a mask chuck 13. Each mask chuck 13 isalso transparent in the active area for patterning. Substrate chuck 14,which generally is not transparent, holds the substrates in place,preferably by vacuum. Substrate chuck 14 is preferably equipped withvacuum shutoffs, and with substrate lifters or with both, to ease theprocess of unloading. Substrate lifters may be configured as simple pins15 which may be caused to rise under inactive or kerf areas of thesubstrate, lifting the substrate panel out of influence of the substratechuck vacuum, presenting the substrate panel for unloading. Thepatterning radiation passes from laser 7, through beam tunnel 16 as beam17. Beam 17 passes through the transparent window 18 and the transparentor open window of mask chuck 13, through mask 3 and projection optics 1to substrate panel 4. FIGS. 1-3 should be considered together. FIG. 1shows the system. FIG. 2 shows details of stage 5 and projection optics1, which are shown with less detail in FIG. 1. FIG. 3 shows details20-29 of placement mechanism 8 which is also shown in FIG. 1.

Loader/Flipper/Forwarder/Unloader Robot

FIG. 3 Is a perspective view of the substrate panel handling robot, thefeeder/flipper/forwarder (loader/unloader) in a preferred embodiment.The substrate panel handling robot was not shown in FIG. 2. Otherconfigurations of substrate-handling devices, such as air jets, rollersor edge grippers, may also be effective, depending upon type ofsubstrate, the type of substrate chuck and the type of loader/unloader.

The stage subsystem works to lock a plurality of masks and substratepanels (positions for two of each are shown in FIG. 1) on the carriage 5of the stage 2, typically by vacuum. The stage subsystem also works tomove those masks and substrate panels in a scanning pattern of motionwith respect to projection optics 1, as is shown in U.S. Pat. No.5,923,403, Jain, cited above in the prior art section. A mask andsubstrate panel are scanned simultaneously, with registration guaranteedby having mask and substrate panel locked to the common stage carriage 5for simultaneous scanning motion. Preferably, scanning is by a smallhexagonal field, in the complementary overlapping mode taught by U.S.Pat. No. 4,924,257, Scan and Repeat High-Resolution Lithography System,Jain, May 8, 1990.

During repetitive operation as shown in FIG. 1, the first substratepanel SP1 is shown as if it had been previously scanned on its reversesurface, flipped over, repositioned to its present position, and scannedon its obverse surface, ready to be unloaded to the supply/return rack6. Substrate panel SP2 has been positioned in the reverse-side positionon the stage carriage 5. The system is now shown poised near thecompletion of a patterning scan of substrate panel SP2 (reverse surface)according to mask 3 _(r).

After the substrate panel SP2 (reverse surface) has been patterned,substrate panel SP2 is flipped and repositioned for patterning theobverse according to mask 3 _(o). Substrate panel SP2, during or afterthe flipping motion, is loaded into the obverse-patterning station forpatterning of substrate panel SP1. This operation continues until theproduction run is finished.

Method of Operation

The above discussion postulates repetitive operation during anintermediate period of the production run. The following paragraphs willgive some detail of beginning and finish of the production run.

Steps −1 & 0—Readiness, Reverse Patterning of SP2

At the beginning, (step=−1), the stage carriage 5 is empty of substratepanels but has obverse-mask 3 o and reverse-mask 3 _(r) locked in theiroperative positions. A pre-load step may load a substrate panel in eachof the patterning work stations 3 _(o) and 3 _(r).

Step 0 takes place after substrate panel SP2 has been loaded with itsreverse surface facing the radiation beam passing through the reversemask 3 _(r).

At this time the stage carriage is fully loaded with two substratepanels, ready for the repetitive operation discussed above, and reviewedin the paragraph following this paragraph.

Step 1—Reverse Patterning of SP2 & Obverse Patterning of SP1

There are substrate panels at the reverse-patterning work station 4 rand at the obverse-patterning work station 4 o. Scanning takes place toplace pattern images 4 r and 4 o on surfaces of substrate panels SP2 andSP1, respectively. When the scan has been completed, substrate panel SP1is ready to be unloaded, substrate panel SP2 is ready to be flipped, andsubstrate panel SP2 is ready to be repositioned at the obverse workstation, with its obverse facing the optical beam from the appropriatemask with pattern 3 _(o).

Final Step—Emptying

At the finish, the reverse work station is empty and the obverse workstation presents the last panel in the production run, substrate panelSPn obverse, for patterning. This panel is scanned for patterning, andthen unloaded, completing the production run.

Simplified Embodiments

In a supersimplified embodiment, the reverse patterning station and theobverse patterning station are not separate, but their functions arecombined at a single, two-side work station. There is preferably asingle mask, the pattern of which ordinarily must be replicated on bothsides of the substrate panel. After scanning, the substrate panel mustbe flipped (without forwarding) and repositioned, at the two-side workstation, for patterning of the other surface of the substrate panel.Loading and unloading are as discussed above.

As another alternative, the mask must be changed after each panelsurface has been scanned. This may be done manually, or may beaccomplished by a mask chuck shuttle, by a carousel or by aloader/unloader from a n adjacent mask rack.

This loader and unloader may be any of several available substrateloaders which are currently marketed, or the load/unload functions canbe handled by the same robot which accomplishes flipper/forwarderfunctions.

FIG. 4 is a perspective view of a simplifiedflipper/forwarder(loader/unloader), a single all-purpose pick-and-placerobot with flipping capability. The flipper/forwarder, in thisembodiment, is also used for loading and unloading. It addresses thesubstrate panel at the reverse work station, and flips the substratepanel over as it forwards It to the obverse work station. Theflipper/forwarder preferably grasps the substrate panel by its sides orin the kerf areas, so as not to damage the photoresist layers and tostay out of the way when the substrate panel is transferred to the stageplatform. If the photoresist is protected by a transparent cover sheet,the flipper/forwarder may be a vacuum grabber that touches the coversheet.

The positioned and repositioned substrate panels may require standardaligning techniques prior to pattern scanning.

FIG. 4 shows the motions of a preferred flipper/forwarder robot, whichmoves by an in-plane sliding motion, once the stage carriage has beenwithdrawn by stage action (or once the stage carriage has been leftbehind by vertical or horizontal motion of the robot holding thesubstrate panel). The sliding motion and the previous work station forthe substrate panel are shown in dashed lines. With sufficient clearanceabove or alongside the stage carriage, the substrate panel 30 is flippedover (inverted) and forwarded to the subsequent work station 31 as shownby the small curved arrow and the solid lines. The 180° rotation of axle32 provides the motion.

FIG. 5 shows the motions of an alternative in-station flipper robot,which moves by an in-plane sliding motion of substrate panel 33, oncethe stage carriage has been withdrawn by stage action (or once the stagecarriage has been left behind by vertical or horizontal motion of therobot holding the substrate panel. The sliding motion and the previouslocation 34 of the substrate panel are shown in dashed lines. Withsufficient clearance above or alongside the stage carriage, thesubstrate panel is moved out of the way of the stage carriage, flippedover. (inverted) by 180° rotation of axle 35 as shown by the smallcurved arrow, and returned, inverted, to the same action station (dashedlines) from the intermediate location shown by the solid lines.

Loading, positioning, forwarding and unloading the substrate panels areshown in ways suggesting pick-up and pass-off of each panel. Variousslide forwarding and carousel forwarding mechanisms may also be used,with or without the cooperation of the stage carriage.

Flipping the substrate panels is shown by wrist rotation separate fromthe forwarding action. Other actions are also possible, such as elbowaction or canted-loop action, where forwarding is achieved during theflip. If the substrate panels have sufficient flexibility, flipping andforwarding may be accomplished using a series of rollers to achieve acanted-loop path. The substrate panel must be lifted off itsvacuum-locked position on the stage carriage, for the patterning of theobverse surface, and then flipped over and forwarded to the actionstation at the same or at the next substrate chuck position on the stagecarriage.

METHOD OF REPETITIVE TWO-SIDED PATTERNING

Step 1=Unload two-side finished substrate panel from obverse patterningstation.

Step 2=Flip reverse-side patterned substrate panel from reversepatterning station.

Step 3=Forward to obverse patterning station for presentation of obversesurface.

Step 4=Load blank substrate panel into reverse patterning station.

Step 5=Scan flipped reverse-side-finished substrate panel at obversepatterning station and scan blank substrate panel at reverse patterningstation.

(Repeat Steps 1-5.)

[Note that Steps 2 and 3 above can be combined. See followingdiscussion.]

METHOD OF REPETITIVE TWO-SIDED PATTERNING WITH FLIPPER/FORWARDER

Step 1=Unload two-side finished substrate panel from obverse patterningstation.

Step 2=Flip and forward obverse-side finished substrate panel, in asingle, complex motion, with the reverse-side finished substrate panelending at the obverse patterning station, presenting substrate panelobverse-side.

Step 3=Load blank substrate panel into reverse patterning station.

Step 4=Scan flipped reverse-side finished substrate panel at obversepatterning station and scan blank substrate panel at side-1 reversepatterning station.

(Repeat Steps 1-4.)

METHOD OF REPETITIVE TWO-SIDED PATTERNING AT A SINGLE STATION, WITHFLIPPER/FORWARDER, DUAL-WAVELENGTH PHOTORESISTS, DUAL-WAVELENGTHRADIATION and TWO-MASK SHUTTLE

Preparatory Steps=Arrange blank substrates alternatively reverse-side upand obverse-side up, reverse-side having photoresist optimized for afirst wavelength, and obverse-side having photoresist optimized for asecond wavelength, load obverse-side-up substrate in obverse patterningstation and obverse-side-up substrate in obverse patterning station,pattern loaded substrates by scanning, and arrange reverse-side andobverse-side masks on a shuttle on the stage carriage;

Step 1=Unload reverse-side & obverse-side finished substrate panel, ifany be present, from obverse patterning station;

Step 2=Flip and forward reverse-side-finished substrate panel, if any bepresent, in a complex motion, with the reverse-side-finished substratepanel ending at the obverse patterning station, presenting substratepanel obverse-side;

Step 3=Load blank substrate panel into obverse patterning station;

Step 4=Scan flipped reverse-finished substrate panel at obversepatterning station and scan blank substrate panel at reverse patterningstation;

(Repeat Steps 1-4.)

Alternatively, a system can feature a substrate loader/unloader/flipperthat could hold two substrates simultaneously. The operator loads twosubstrates onto the tool at one time, exposes both, flips both (andtransfers both substrate panels to opposite work stations in theflipping step, exposes, both (opposite sides) and unloads both.Substrates could be arrayed alternatively, first side up/second side up,if necessary.

What is claimed is:
 1. Apparatus for controlled two-sided mask patternimaging of substrate panels, each substrate panel having two surfaceswhich may be designated obverse and reverse, said apparatus usingloading means for positioning a substrate panel, having unloading means,having at least one mask station and having control means to directimaging of a mask pattern onto a surface of a substrate panel,comprising: a) stage mechanism controllable to provide motions includingscanning motions and positioning motions to a movable carriage, saidcarriage having substrate chuck means at positions including obverse andreverse imaging positions; b) a single-approach projection subsystemcontrollable to scan a selected mask image to the obverse surface of asubstrate panel at said obverse imaging position and to scan a selectedmask image to the reverse surface of a substrate panel at said reverseimaging position; and c) movable placement mechanism having controllablecapability for taking a substrate panel from said obverse imagingposition, inverting said substrate panel and returning said invertedsubstrate panel to said stage mechanism movable carriage at said reverseimaging position for a subsequent imaging scan of the reverse surface ofsaid substrate.
 2. Apparatus for repetitive two-sided mask patterning ofsubstrate panels, according to claim 1, wherein said movable placementmechanism and said stage mechanism are controlled forfeeder/flipper/forwarder/unloader functions.
 3. Apparatus for controlledtwo-sided mask pattern imaging of substrate panels, each substrate panelhaving two surfaces which may be designated obverse and reverse, saidapparatus using loading means for positioning a substrate panel, havingunloading means, having at least one mask station and having controlmeans to direct imaging of a mask pattern onto a surface of a substratepanel, comprising: a) stage mechanism controllable to provide motionsincluding scanning motions and positioning motions to a movablecarriage, said carriage having substrate chuck means at an imagingposition; b) a single-approach projection subsystem controllable to scana selected mask image to the obverse surface of a substrate panel at animaging position; and c) movable placement mechanism having controllablecapability for taking a substrate panel from said obverse imagingposition, inverting said substrate panel and returning said invertedsubstrate panel to said stage mechanism movable carriage substrate chuckmeans at said imaging position for a subsequent imaging scan of thereverse surface of said substrate.
 4. Apparatus for repetitive two-sidedmask patterning of substrate panels, according to claim 3, wherein saidmovable placement mechanism and said stage mechanism are controlled forfeeder/flipper/unloader functions.